Hyperactive boys were treated with up to 15 mg/day of clorgyline, a selective Monoamine Oxidase A Inhibitor, or amphetamine (0.5/mg/kg). A second group was treated with tranylcypromine (Parnate) up to 15 mg/day. Behavioral measures include motor activity, vigilance and parent and teacher behavior ratings. Biological measures include urinary MHPG, PEA and platelet MAO. The aim of the study is to elucidate neurotransmitter mechanisms in amphetamine's efficacy in hyperactivity.